Molding apparatuses, such as injection molding machines and die-cast machines, comprise a mold clamping apparatus in which a mold, consisting of a fixed mold and a movable mold, is to be mounted, and an injection apparatus. The mold clamping apparatus includes a fixed platen to which the fixed mold is to be mounted, and a movable platen to which the movable mold is to be mounted. There are various types of known mold clamping apparatuses. A typical one is a toggle-type mold clamping apparatus which moves a movable platen back and forth along tie bars through extension/contraction of a power-driven toggle link mechanism, thereby closing, clamping and opening a mold.
The toggle link mechanism of such a toggle-type mold clamping apparatus is a link mechanism connecting a pressure-receiving plate, a crosshead having a ball nut, and a movable platen. The ball nut is in engagement with a ball screw which is driven by an electric motor, so that rotation of the ball screw is converted into linear movement of the crosshead. The toggle link mechanism can thus be extended/contracted to move the movable platen back and forth.
When the toggle link mechanism of the toggle-type mold clamping apparatus is locked up to clamp the mold, a reaction force acts on a link housing provided in the pressure-receiving plate. Therefore, improvements have heretofore been made to a support structure for the ball screw or to a support structure for maintaining the posture of the crosshead.
For example, the ball screw is cantilever-supported by the link housing; the front end of the ball screw is not supported. Therefore, flexure or deflection is likely to occur in the ball screw upon actuation of the toggle link mechanism, which may result in a decrease in the life of the ball nut. In order to prevent flexure or deflection of such a ball screw, Japanese Patent Laid-Open Publication No. 2003-33955, for example, has proposed a support structure provided with a support bearing for supporting the front end of the ball screw.
In the toggle-type mold clamping apparatus, upon the lock-up operation which generates a mold clamping force, a reaction force to the mold clamping force is transmitted to the crosshead via the link mechanism. The posture of the crosshead then becomes unstable and the crosshead can sometimes tilt if the rigidity of a support structure for the crosshead is low.
In view of this, in such a conventional toggle-type mold clamping apparatus, a support structure for the crosshead has been proposed which includes guide bars for guiding back-and-forth movement of the crosshead, the guide bars each being supported by an arm of a link housing.